Surface mining and other types of geological exploration utilize drilling apparatus to bore holes in the earth's surface. The drilling apparatus employs a plurality of drill pipe sections, normally tubular steel pipe sections, which come in a variety of lengths with a forty-five foot length being somewhat typical. These pipe sections, or drill steels as they are called, are connected one to another by providing cooperating threads at adjacent ends of the pipe sections such that relative rotational movement between the pipe sections causes the pipe sections to become threadedly engaged. The uppermost pipe section on a string of drill steels is attached to the power transmission of the drilling apparatus through a device known as a thread saver which is simply a short length of tubing which is threaded at both ends and serves to protect the threads of the expensive transmission from damage thereby averting costly repairs of the transmission. Typically each drill steel and the thread saver are tubular conduits through which air, water or other fluids may be injected into the bore hole for various purposes, depending on the nature of the drilling operation being carried out.
When the drill string is to be removed from the bore hole the steels are raised and each pipe section must be unthreaded from its subjacent pipe section to facilitate removal. This may be accomplished by engaging the subjacent pipe section with apparatus known as breaking dogs or other devices to arrest rotation of the subjacent pipe section from the uppermost pipe section to be unthreaded while rotating the transmission and the upper pipe section in a direction to unthread the upper pipe section from its subjacent pipe section. Inasmuch as great forces are generated in drilling operations, the threaded connections between the pipe sections are increasingly tightened by the rotation of the drill string in the earth. Consequently the separation of the pipe sections or "breaking" of the steels is not easily accomplished. Inasmuch as the threads connecting the pipe sections to each other and also connecting the thread saver to the upper pipe section must all be inclined in the same direction in order for the string to rotate, it will be seen that arresting rotation of the pipe section subjacent the upper pipe section places the breaking stress on the remaining threaded connections at each end of the upper pipe section, that is at the joint between the thread saver and the upper pipe section and at the joint between the upper pipe section and the pipe section subjacent thereto. Frequently the break occurs at the juncture of the thread saver and the upper pipe section rather than at the juncture of the pipe sections and consequently the removal of the upper pipe section from the string is more complicated inasmuch as the upper pipe section remains securely fastened to the pipe section subjacent thereto and the remaining pipe sections in the ground while being free from the motive force required to rotate the upper pipe section to break its connection to the subjacent pipe section.
When the break occurs at the thread saver the operation of the drilling apparatus comes to a halt until a welder can be brought to the scene to heat the connection between the upper pipe section and the pipe section subjacent thereof in order to expand the metal and thereby decrease the frictional resistance to breaking at this joint in order to improve the likelihood that the break will occur between the pipe sections as desired. Obviously, the mining operations are greatly impeded by this delay. Numerous other methods such as large wrenches which grasp the exterior of the drill steel have been employed in an effort to overcome this problem; however such wrenches are susceptible to contamination by dirt, dust and other foreign matter which is common at the drill site and are therefore considered to be of little use. Also the forces generated on these external devices in attempting to break the steel at these threaded junctions is considerable and presents a safety hazard to any crew members in the proximity of the wrenches while in operation.
When conventional devices are utilized to break a joint in the drill string, the normal procedure is to engage the drill string with the breaking dogs as noted hereinabove and to then rotate the uppermost length of pipe with the transmission. This of course creates great wear and tear on the breaking dogs and consequently requires their frequent replacement which is in and of itself a costly and time-consuming job. Additionally when the breaking dogs engage the lengths of pipe which are rotating it creates great stress on the transmission of the drive units which of course leads to substantial wear and tear particularly when severe impact or shocks occur as are likely to happen in such an operation. Therefore conventional methods of breaking the steel not only are inconvenient in that the steel may break at the wrong junction, they are also harmful to the machinery and serve to shorten the useful life of the transmission and drive apparatus.